This invention relates to the field of glass containers and more particularly to a container of improved mechanical service strength and shatter resistance having an outside containment coating constituted by a plastic film.
In the container industry, substantial efforts have been devoted to developing methods for improving the impact and burst strength of glass containers without significantly adding to the cost of producing such containers. Improvement in impact and burst strength can provide not only important economic benefits through reduced attrition, but can also make critical contributions to the personal safety of those who fill, handle and use glass containers.
A substantial effort has been underway in the art to develop containment coatings which improve the resistance of a glass beverage container to impact or burst failure. In recognition of the fact that prevention of such failure under all possible conditions of handling is an objective whose economical attainment is difficult, if not impossible, much effort has also been devoted to the development of means for mitigating the consequences of the failure of a glass container. Thus, important objects have been to minimize both the degree of fragmentation and the extent of scatter of the fragments produced when a glass bottle fails.
Each of the properties of the impact resistance, burst strength, resistance to fragmentation and minimization of scatter is particularly important where a beverage bottle is used for packaging a carbonated beverage. Bottles for carbonated beverages are routinely exposed to internal pressures in the range of about 50 psig. If and when such a bottle is broken, the resulting fragments, particularly if they are very small, can be propelled at high velocity by the carbon dioxide which is released. If these fragments strike a person, serious injuries may result. Occasionally a beverage bottle explodes due to the force of internal pressure alone. Serious injuries have been caused by exploding beverage bottles.
As a means of improving the mechanical properties of beverage bottles in the above-noted respects, it has been proposed to provide such bottles with a "containment" or protective coating. Compositions and processes are known, for example, which may be utilized to provide a glass container with a relatively thick coating of styrene foam. Styrene foam coatings are esthetically undesirable since they are white and opaque, thus preventing observation of the contents of the bottle. Glass containers also are known to have an outer lubricating film of polyethylene over an intermediate layer of a metal oxide such as a tin or titanium oxide for abrasion protective purposes. However, these do not in themselves provide satisfactory impact resistance and containment.
As a result of the conditions encountered in the filling, handling and usage of a beverage bottle, a containment coating must meet a number of diverse criteria in addition to the mechanical properties noted above. Thus, in order to maintain its own integrity and effectiveness, the coating should be substantially resistant to abrasion. To avoid interference with visual observation of the bottle's contents, the coating preferably possesses a high degree of clarity. To survive general usage and, in particular, to survive bottling plant processing, the coating should be resistant to both alkali and hot water. In order to minimize fire hazards in the process of coating the bottle, the containment coating composition should not include significant proportions of flammable organic solvents, and desirably should be water based. It is also desirable that the containment coating be subject to incineration without generating significant quantities of either toxic or obnoxious gases. Finally, the containment coating must be inexpensive to formulate and apply, failing which its use and application to beverage bottles is not feasible or practically economic.
A glass container having a generally satisfactory acrylic containment coating is described in the copending and coassigned application of McCoy and Sharpe Ser. No. 189,392 filed Oct. 14, 1971. The coatings described in this application have a high degree of clarity and alkali resistance and are also characterized by a relatively high degree of lubricity which minimizes damage which might otherwise be incurred in the handling incident to the bottle manufacturing process. The coatings described in the aforesaid application also provide protection against abrasion, impart improved burst and impact strength and reduce the extent of fragmentation and scatter in the event that a bottle to which whey have been applied does fail. Although substantially superior to bottles provided with many previously known coatings, the bottles described by McCoy and Sharpe still have a somewhat limited mechanical service strength and the degree of fragmentation and scatter is still significant when gas-pressurized bottles produced in accordance with their invention fail under severe impact. An important need has, therefore, remained in the art for a glass container having an improved containment coating so that the mechanical service strength and shatter resistance is substantially improved over glass containers previously known.